A trench transistor device, such as a trench MOSFET (metal oxide semiconductor field effect transistor) or a trench IGBT (insulated gate bipolar transistor), is a vertical transistor device that includes a semiconductor body with a first and a second surface in which at least one source region, at least one body region, a drift region, and a drain region are integrated. In an IGBT the source and drain regions are also referred to as emitter regions, and the body and drift regions are also referred to as base regions.
Usually, the source region and the body region are integrated in the region of the first surface, while the drain region is integrated in the region of the second surface and separated from the body region by the drift region. At least one gate electrode, which serves to switch the component on and off, is arranged in a trench of the semiconductor body in the region of the first surface. The source region is electrically contacted by a source electrode which is usually arranged above the first surface and which is electrically insulated from a gate terminal (gate pad), with the latter contacting the gate electrode. The drain region is electrically contacted by a drain electrode which is usually arranged above the second surface.
Vertical transistor components of this kind can be mounted on a carrier with their second surface facing towards the carrier. In such an arrangement the carrier can serve as a drain terminal of the transistor component and can further serve as a cooling element for dissipating heat generated in the semiconductor body. When the vertical transistor element is operated as a switch, heat is mainly generated in its active regions, like body and drift regions. Since these active regions are arranged close to the first surface while the cooling element is arranged on the second surface, there is a relatively high thermal resistance resulting from those regions of the semiconductor body which are arranged between the pn-junction and the second surface. The thermal resistance could be reduced by arranging a cooling element on the first surface. However, such cooling element would short-circuit the gate and the source electrode which are both arranged at the first surface.
There is, therefore, a need for a semiconductor device which has better properties in terms of dissipating heat from the semiconductor component.